The quick burial by volcanic ash highly preserved the towns buildings and other artifacts Products of Volcanic Eruptions. • Lava Flows: – Basaltic / Mafic Lava. PDF | SynonymsMagmatic eruptions; Volcanic explosionsDefinitionVolcanic Eruptions. The expulsion of liquid rock (magma) – explosively or. Volcanic eruptions. GEOS – InSAR and its applications (Fall ). Advantages of InSAR for monitoring natural hazards. SAR interferometry provides.
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Volcanoes and Volcanic Eruptions. Magmas and Lava. Since volcanic eruptions are caused by magma (a mixture of liquid rock, crystals, and. What are two kinds of volcanic eruptions? • How does the composition of magma affect eruptions? • What are two ways that magma can erupt from a volcano?. Identify volcanic processes seen in photographs. ○ Understand that, during an eruption, volcanic processes often occur simultaneously or.
The densest part of the plume, directly above the volcano, is driven internally by gas expansion.
As it reaches higher into the air the plume expands and becomes less dense, convection and thermal expansion of volcanic ash drive it even further up into the stratosphere. At the top of the plume, powerful prevailing winds drive the plume in a direction away from the volcano.
These highly explosive eruptions are associated with volatile-rich dacitic to rhyolitic lavas, and occur most typically at stratovolcanoes.
Eruptions can last anywhere from hours to days, with longer eruptions being associated with more felsic volcanoes. Although they are associated with felsic magma, Plinian eruptions can just as well occur at basaltic volcanoes, given that the magma chamber differentiates and has a structure rich in silicon dioxide. They are also similar to Hawaiian lava fountains in that both eruptive types produce sustained eruption columns maintained by the growth of bubbles that move up at about the same speed as the magma surrounding them.
It is the model Plinian eruption. Mount Vesuvius has erupted several times since then.
Its last eruption was in and caused problems for the allied armies as they advanced through Italy. The eruption of Mount St. Helens in The past years have been a pattern of violent initial eruptions of pumice followed by prolonged extrusion of basaltic lava from the lower part of the volcano.
RiskScape is presently scenario-driven, although in the future it is planned to have a probabilistic component for probabilistic risk evaluation. To date, it has been used in New Zealand and in the wider Asia-Pacific region. A key feature of RiskScape is its modular structure Fig.
At present the multiple volcanic hazards are treated independently, but the intent is to modify this in the future. Thus, there is no current mechanism for evaluating compound volcanic impacts — e.
Types of volcanic eruptions
As such, in the instance of modelling the effects of multiple volcanic hazards, at this stage care needs to be taken to avoid double-counting losses. Additionally, RiskScape currently assumes all impact happens during initial exposure — there is no consideration of potential impacts caused by delayed clean-up or long-term effects.
RiskScape calculates impacts to assets on an individual asset-by-asset basis. For each asset the hazard intensity at the site is evaluated against the vulnerability or fragility function to estimate the impact.
If the vulnerability model is deterministic no uncertainty then the results are reproducible as the mean damage ratio is always evaluated. If the model incorporates uncertainty in the damage ratio then the user can evaluate the mean damage ratio, or sample from the uncertainty distribution damage ratio as a function of intensity using a Monte Carlo simulation method. Fragility functions are inherently probabilistic and the user can calculate the most likely damage state or sample from the distribution of damage states using Monte Carlo simulation methods to generate a distribution of damage states.
For both approaches the individual asset results can be assessed or aggregated to a user-defined aggregation unit such as suburb, or census administration units.
For further details of the RiskScape model, the reader is referred to Schmidt et al. Hazard module Within the RiskScape framework, the hazard module sets the extent and intensity of the hazard of interest. For some hazards, such as earthquake shaking intensity or volcanic tephra deposition, the user can select the source and input parameters — for earthquakes this is the epicentre and magnitude, whereas for volcanic tephra deposition this is the volcano, eruption size, and wind model.
RiskScape then provides on-the-fly modelling of the extent and intensity of the hazard — shaking for earthquakes or deposit thickness for volcanic ash. For other hazards which have greater computation requirement for their associated hazard models, such as flooding or lava flows, RiskScape does not provide on-the-fly modelling — rather, the user must upload or select a pre-uploaded file of the extent and severity of the hazard.
Due to computational demands, it is unlikely on-the-fly modelling for these hazards will be provided in the short term. Hazard layers may be input in any coordinate system the user must specify which one and for anywhere in the world. As RiskScape is a scenario based tool, the magnitude-frequency distribution of a given hazard is not required. However, the probability of occurrence of a particular scenario is useful to know, especially when impacts between hazards are compared in a multi-hazard risk assessment using RiskScape.
Hazard intensity is a key parameter input to vulnerability models. In the example of floods and tsunami, velocity which may at times act as a proxy for discharge may be most strongly correlated to damage, yet often only high water levels are available post-event; in such cases while the ideal HEMU would be velocity, high water levels are the HEMU used in the majority of fragility and vulnerability functions.
As RiskScape was selected as the primary way to evaluate volcanic risk for Auckland, New Zealand by the Determining Volcanic Risk for Auckland DEVORA research programme, certain decisions regarding hazards and default parameters have been made considering the Auckland context, explained further when appropriate in this paper.
The extent of c is indicated with a black box. We did this by reviewing available literature for which HEMUs cause damage or reduced functionality for a wide range of assets types, including buildings, people, and critical infrastructure.
Ash Impact Posters
The HEMUs which were relevant for impact to the greatest number of asset types were then shortlisted. We then considered the ease of realistically modelling or determining each HEMU. We then selected the HEMU on the balance of relevance and determinability.Gates, A. The understanding of earthquake risk in New Zealand is well advanced through national level studies by Cousins and Dowrick et al.
Earth 2nd ed.
The Magill and Blong a , b papers compared risk from several hazards in addition to volcanic eruptions, including flooding and climate change. Marvin; C.
Archived from the original on 7 July As such, in the instance of modelling the effects of multiple volcanic hazards, at this stage care needs to be taken to avoid double-counting losses.
We then considered the ease of realistically modelling or determining each HEMU.